Got a question for you guys.  I just bought a brand new 3.5 hp Mercury 4-stroke and tested it for the first time today.  It took about a dozen pulls to get it started but then finally started.  We drove for about 25 minutes or so between idle and about half or just under half throttle and it suddenly got weaker...weaker...then boom, shut off.  Another dozen or so pulls later, it was back working again.. we were cruising at about half speed and then weaker...weaker...weaker....shut off.

Then, something even stranger happened.  When I restarted the engine, it would REV UP quite a bit without me throttling up AT ALL (it was still on the "restart" part of the throttle.  Any idea why this would happen?  Or how it could happen?

Now, I know nothing about outboards (as this is my first...EVER) but I'm a little concerned... Is is possible that I simply need to be more patient and give it more "burn in" time OR does this sound like a bad motor (even though it's new).

Any help at all would be greatly appreciated.  

Thank you all so much!

by the way, I said "burn in" earlier.... I meant "break in" obviously... Here's a follow up question..  You know the screw at the top of the gas tank that is for ventilation?  How "open" does that screw have to be?  I noticed that you can unscrew it for a while before it stops unscrewing

Hi, Be sure the vent is open on the gas tank. I had this happen to me once. A new gas can and I did not realize there was a little vent cap on top of the filler cap. We were running along just fine and it just died and would not crank. I noticed the tank looked like it had sunk in. I saw the little vent cap and opened it and the tank went back to normal shape. After that the first pull and it started right up and ran fine. This was on a two stroke motor, but I don't think that would be any different than a four stroke. Good luck and I hope it is something simple.

Jim

Keep that vent all the way open. The engine needs to take in fuel and it can't suck very hard so if there's any negative pressure it won't take any in and it will die just like you described.

Made sure the vent was wide open and still having the same issue.  I can run for about 10 minutes....then the motor starts slowly sounding weaker until it dies completely.

I just can't believe a BRAND NEW motor is doing this!  And this is a mercury, not some cheap-o brand.  UGH!

How is the choke? You leaving it open, not opening it, opening it for start then closing?

M Starr:  At this point I must confess near total ignorance about choke and what this does to the engine, etc.  However, Mercury says leave it open to start, then move half way till engine "warms up" (how long is that?) and then push it all the way in.  I practically NEVER get the motor started doing this.  I can open it all the way, then crank it, but as SOON as I try to push it in, the engine dies.  

The ONLY time I seem to be able to crank it relatively consistently (after about 10 pulls, and 30 sec - 3 min rest) is with the choke pushed in all the way and the throttle set to "restart".  This will crank (nicely) and give me about 10 -15 minutes of run time before getting weaker, and weaker, and weaker, and dying again... requiring me to go through the whole process again.     Ideas?

Thats why I was asking. I have a mercury 8 hp 4 stroke. It is my first OB as well. I kept forgetting to close the choke when I got it going and it would run like a pig, especially at idle. Then it would take me 300 pulls to get it started. I can't tell you the foul language I sent across the lake.

What I found now, is I will get it started at full choke, then hit the button on the side to disengage the trans and run it at slightly higher RPMs for a bit. Once I can close the choke completely without it sputtering, I do so and it runs like a champ and 9 times out of 10 will start on the first pull.

If I forget (and I still do from time to time) it is a PITA. I did notice, when I used to leave that vent closed or not open enough on the gas tank the primer bulb would be the first thing to sink in, followed by the tank a little then a nice annoying stall.

It sound like you might have an air leak in the hose. Make sure the bulb stays firm. If you run it and it starts to die try squezing the bulb and see if it starts to run properly.

The hoses have o rings in the fittings that can leak and the hose or bulb could be cracked.

 

Forgive my embarrassing ignorance, but I'm not sure what bulb you guys are referring to.  Keep in mind this particular model (3.5 hp) has the gas tank built in.

Sounds to me like the choke is out.  Push it back in once its started and idling.

Return your new motor and get you a replacement motor that wants to work.

The bulb the guys are talking about is the one that in the middle of a fuel line that connect the outboard to the remote fuel pump.  This bulb is used to prime the motor with fuel before starting.  Your outboard has a built in tank their fore their will be no primer bulb.  Unless it has one similar to a lawn mower engine that you depress to prime the motors carb.

Honestly if you do play with the choke and still get the same issue, take it back. Have them try it out and see if they see the same thing. Make them prove to you that the motor works.

Take it back to where you bought it...it should be fixed or replaced for free, theres no excuse for a new motor stuttering.

Forgive my embarrassing ignorance, but I'm not sure what bulb you guys are referring to. Keep in mind this particular model (3.5 hp) has the gas tank built in.

Don't ask for forgiveness, it's not necessary. We have all been in your position and we all want to help you.

If the tank is built in then you would not have a bulb. A bulb is found on the hose between an external tank and the engine. It is used to pump gas from the ank to the motor.

Is there an air vent on your tank? The vent needs to be open when your running. The fact that the engine revs up at times sounds like fuel starvation. Mine does that when I run the fuel out of the carb.